Prevalence and Time
Trends

Nationally representative
U.S. health examination surveys, in which weight and height were measured in
samples of the population, date back to 1960. Beginning with the Second
National Health and Nutrition Examination Survey (NHANES II) (1976-1980), the
definition of overweight that has been used to compare these epidemiologic
surveys has been a statistical one that corresponded to the 85th percentile of
body mass index (BMI) for men and women aged 20 through 29 years in NHANES II
with no particular relation to a specific increase in disease risk (45). Adults in these surveys have been
categorized as overweight with a BMI
27.8 kg/m2
for men and
27.3 kg/m2
for women (45). The rationale for using
persons aged 20 through 29 years as the reference population is supported
largely by the observation that the increases in body weight after age 29 that
commonly occur with aging are attributable primarily to fat accumulation (46, 47). However, the BMI levels used for
the definition of overweight and obesity are somewhat arbitrary, since the
relationship between body weight and disease risk is continuous with the
exception of the extremely underweight: disease risk increases as weight
increases.

Figure 1 depicts data from
several NHANES surveys using the panel's definition of overweight as a BMI of
25 to 29.9 kg/m2 and of obesity as a BMI of
30 kg/m2.
From 1960 to 1994, the prevalence of overweight increased slightly from 37.8 to
39.4 percent in men and from 23.6 to 24.7 percent in women (National Center for
Health Statistics/CDC) (48). In men and women
together, overweight increased from 30.5 to 32.0 percent (48). During the same time period, however, the
prevalence of obesity increased from 10.4 to 19.9 percent in men and from 15.1
to 24.9 percent in women. In men and women together, obesity increased from
12.8 to 22.5 percent. Most of the increase occurred in the past decade. In
addition to adults, obesity in U.S. children increased markedly as well (49) (See Appendix
III), and, if unchecked, portends an even greater increase in adult obesity
in the future.

Table II-1shows the combined
prevalence of overweight and obesity, defined as a BMI of
25.0 kg/m2,
among persons aged 20 to 80-plus years, by age, race/ethnicity, and gender in
the United States from 1960 to 1994 (48). The
increase in overweight and obesity appears to have occurred among U.S. adults
across all ages, genders, and racial/ethnic groups. The most recent NHANES III
surveys, conducted from 1988 to 1994, reported that 59.4 percent of men and
50.7 percent of women in the United States are overweight or obese. The
prevalence is much higher in non-Hispanic Black women (66.0 percent), in
Mexican-American women (65.9 percent), and in Mexican-American men (63.9
percent).

Using the definition of
obesity as a BMI of
30 kg/m2,
Table II-2 shows that in the United States, 19.5 percent of men and 25.0
percent of women are obese (48).The
prevalence of obesity is much higher in minority women, being 36.7 percent in
non-Hispanic Black women and 33.3 percent in Mexican-American
women.